The development and operation of active sound and vibration control systems requires a wealth of information and technology in several areas of engineering and science. It requires skill, technology and knowledge relating to the physical system being controlled (i.e. the plant), to control techniques, to mechanical and electronic control hardware, and to computer programming.
Consider, for example, an active sound control system in which the physical system being controlled is an acoustic plant receiving input acoustic waves. Canceling acoustic waves are introduced into the plant to destructively interfere with and cancel the input acoustic waves so that the amplitude of output acoustic waves from the plant are reduced. In such an active sound control system, it is typical to sense input acoustic waves with one or more input transducers (e.g. input microphones) and sense output acoustic waves with one or more error transducers (e.g. error microphones). The input transducers supply an input or feedforward signal to an electronic controller, and the error transducers supply an error or feedback signal to the electronic controller. The electronic controller is programmed with a control model that models the plant and filters the signals from the transducers (e.g. microphones) to generate a correction signal. The correction signal is supplied to an actuator (e.g. a canceling loudspeaker); and, in response to the correction signal, the actuator introduces canceling acoustic waves to destructively interfere the input acoustic waves.
In some ways, active sound control systems are similar to active vibration control systems. Active vibration control systems normally attenuate mechanical vibrations in a mechanical structure, or otherwise restrict unwanted movement of a mechanical structure. Typically, active vibration control systems have transducers that measure or predict mechanical movement in a structure and generate corresponding signals that are transmitted to an electronic controller (e.g. with accelerometers or other means known in the art). The electronic controller is programmed to model the plant (i.e. the structure), and filter the signals to generate a correction signal that is supplied to one or more output actuators (e.g. electromechanical shakers). Forces introduced by the output actuators cancel or lessen the unwanted mechanical movements.
For both active sound control systems and active vibration control systems, it is important that the electronic controller be able to properly model the physical system being controlled (i.e. the plant). In other words, it is important that the electronic controller properly filter input and error signals to generate an appropriate correction signal. It is also important that. the mechanical and electronic control hardware be properly installed and calibrated.
In most applications, the configuration of the control hardware and the configuration of the control model of the plant in the electronic controller need to be customized. Properly customizing the design of an active control system depends on considerations such as the properties of the physical system being controlled (i.e. the plant), the type of outside influences on the physical system, and the required performance of the control system. For instance, some applications require that certain types of control techniques be incorporated into the control model programmed on the electronic controller, while other applications require other types of control techniques. A particularly effective control technique in many applications requires the use of an adaptive recursive filter in the electronic controller.
Since active systems need to react to changes occurring in the physical system or to changes occurring to the inputs into the physical system, there is often a trade-off between the accuracy of the control model programmed on the electronic controller and the speed of the model. This trade-off can be lessened by optimizing the efficiency of executable code implementing the control model on the electronic controller.
The electronic controller is typically programmed by downloading executable code containing a control model and other control system software from a host computer via a communications link. In such a system, the host computer normally communicates with the electronic controller over the communications link even after the electronic controller is programmed. In this manner, the host computer can access the electronic controller in real-time for a variety of purposes that are useful for developing and analyzing the control system. For instance, selected information from the electronic controller can be viewed in real-time on a monitor of the host computer. Also, in some systems certain operation parameters on the electronic controller can be changed or modified by commands from the host computer. This allows users to control the operation of the electronic controller in real-time.
The process of developing appropriate and optimized executable code for the electronic controller normally involves editing computer source code in a text editor on the host computer. Then recompiling and relinking the edited source code on the host computer and downloading the executable code from the host computer to the electronic controller. This reprogramming is done repeatedly until the executable code is optimized, and also properly models the plant and otherwise operates the control system. The iterative process for developing optimized executable code to model the plant and otherwise operate the control system is a formidable task, which is virtually undoable for an engineer that does not know the programming language used on the host computer. Even for an engineer that is an experienced computer programmer, the re-programming process can be time consuming.
Another difficulty with the development and operation of active sound and vibration control systems is that engineers or scientists designing such systems need to be skilled in the use of control system hardware and software, and also need to be skilled in the technical areas relating to the physical system being controlled. For instance, they need skill in control systems, computer programming, and in how acoustics or mechanical vibrations behave in the particular application. Training and educating engineers and scientists so they have a sufficient background in each of these areas takes considerable time and devotion, and in some cases makes the development of sound and vibration control systems cost prohibitive. Sometimes a few engineers and scientists on a development team are sufficiently skilled in all the required areas, but even then it is difficult to train and educate others on the development team.